Single wavelength reflection for leadframe brightness measurement

ABSTRACT

A method for evaluating a leadframe surface includes positioning a leadframe on a measurement apparatus at a first predetermined distance relative to an end portion of a light source of an optical sensor; irradiating a predetermined area on a surface of the leadframe with light having a single predetermined wavelength from the light source; receiving, with a light receiver of the optical sensor, reflected light from the predetermined area on the surface of the leadframe, and converting the reflected light into an electric signal; determining a reflection intensity value of the predetermined area on the surface of the leadframe based on the electric signal; and calculating a reflection ratio of the predetermined area on the surface of the leadframe based on the reflection intensity value and a predetermined reference reflection intensity value associated with the light source.

BACKGROUND

Leadframes are used in most integrated circuit packages. Most kinds ofintegrated circuit packages are made by placing a silicon chip on aleadframe, then wire bonding the chip to the metal leads of theleadframe, and then covering the bonded structure with plastic, usuallyan epoxy-based thermoset compound. A leadframe is essentially a thinlayer of metal that connects the wiring from tiny electrical terminalson the semiconductor chip surface to the large-scale circuitry onelectrical devices and circuit boards. Most leadframes are typicallyproduced on a single, thin sheet of metal by stamping or etching toallow them to be quickly processed on the assembly line.

Prior to incorporating the leadframe in the integrated circuit package,a surface of the leadframe may be subject to various processes includingplating and/or roughening to enhance adhesion between the leadframe andthe epoxy during the packaging process. For example, the leadframesurface may be roughened by treating the leadframe with a chemicaletchant. Further, the leadframe surface may be plated with a noble metalor metal alloy. These processes may be designed with the goal ofreducing the tendency of the leadframe and plastic epoxy to separate asa result of differing thermal-expansion rates between the metal of theleadframe and the plastic of the package following prolonged exposure tomoisture.

Although roughening and plating the leadframe surface may enhanceadhesion properties of the leadframe, it may also affect the color andreflectivity (brightness or glossiness) of the leadframe surface.Further, due to process variations like current density, chemicalconcentration, equipment standards and the like during the leadframeplating and roughening processes, it may be difficult to preciselycontrol the color and reflectivity of the surface of the leadframes fromone batch to the next, thereby creating color and brightnessinconsistencies of the leadframe surface. Still further, such color andbrightness (reflection) variations may be difficult to quantify andstandardize.

Consistency of the color and brightness of the leadframe surface may beimportant in a package production line that heavily relies on patternrecognition. More specifically, in the package production line, machinesfor performing a variety of processes including dispensing epoxy on topof the leadframe surface, die bonding, wire bonding, mount process,molding treatment, strip test process and the like may rely on patternrecognition. For example, in the mount process on the package productionline, a machine may perform pattern recognition based on color andbrightness of the leadframe surface to determine epoxy volume or epoxyshape dispensed on a leadframe surface. Even if there is a slightvariation in the color and/or brightness of the leadframe surface, themachine may not accurately distinguish the leadframe surface from theepoxy and as a result, the pattern recognition process may fail or beperformed incorrectly, thereby resulting in a significant loss ofproductivity and increase in cost on the assembly line.

SUMMARY

The following presents a simplified summary of the disclosed subjectmatter in order to provide a basic understanding of some aspects of thesubject matter disclosed herein. This summary is not an exhaustiveoverview of the technology disclosed herein. It is not intended toidentify key or critical elements of the invention or to delineate thescope of the invention. Its sole purpose is to present some concepts ina simplified form as a prelude to the more detailed description that isdiscussed later.

In one example, a method for evaluating a leadframe surface includes:positioning a leadframe on a measurement apparatus at a firstpredetermined distance relative to a distal end portion of a lightsource of an optical sensor; irradiating a predetermined area on asurface of the leadframe with light having a single predeterminedwavelength from the light source; receiving, with a light receiver ofthe optical sensor, reflected light from the predetermined area on thesurface of the leadframe, the light receiver photoelectricallyconverting the reflected light into an electric signal; determining areflection intensity value of the predetermined area on the surface ofthe leadframe based on the electric signal from the light receiver; andcalculating a reflection ratio of the predetermined area on the surfaceof the leadframe based on the reflection intensity value and apredetermined reference reflection intensity value associated with thelight source.

In another example, a leadframe surface measurement system includes:memory; at least one processor that is coupled to the memory; an opticalsensor including a light source and a light receiver; a measurementstage on which a leadframe is mountable, wherein the measurement stageis movable in three orthogonal axis directions relative to a measurementapparatus base to position the leadframe at a first predetermineddistance relative to a distal end portion of the light source of theoptical sensor, wherein the light source is configured to irradiate apredetermined area on a surface of the leadframe with light having asingle predetermined wavelength, and wherein the light receiver isconfigured to receive reflected light from the predetermined area on thesurface of the leadframe, and to photoelectrically convert the receivedreflected light into an electric signal; and a cantilever assemblymounted on the measurement apparatus base so that a free end of thecantilever assembly is positioned to overhang the measurement stage, thecantilever assembly housing the distal end portion of the light sourceand the light receiver; and wherein the at least one processor executesinstructions stored in the memory to: determine a reflection intensityvalue of the predetermined area on the surface of the leadframe based onthe electric signal from the light receiver; and calculate a reflectionratio of the predetermined area on the surface of the leadframe based onthe reflection intensity value and a predetermined reference reflectionintensity value that is associated with the light source and that isstored in the memory.

In another example, a method of manufacturing a packaged deviceincludes: irradiating light having a single predetermined wavelength ona predetermined area on a surface of a leadframe to determine whether abrightness ratio of the predetermined area is higher than apredetermined minimum brightness ratio threshold; mounting asemiconductor chip on the leadframe responsive to a determination thatthe brightness ratio is higher than the threshold; electricallyconnecting pads on the semiconductor chip with pads on the leadframe;applying a molding compound on the semiconductor chip and the leadframeand curing the molding compound; and singulating each of a plurality ofthe leadframes of a leadframe sheet to manufacture a plurality ofpackaged devices.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1A shows a perspective view of leadframe surface measurementapparatus 100 according to one or more embodiments.

FIG. 1B shows an enlarged perspective view of a light irradiationoperation conducted by leadframe surface measurement apparatus 100according to one or more embodiments.

FIG. 2 shows graph 200A of an incident single wavelength and graph 200Bof reflection intensity according to one or more embodiments.

FIG. 3 shows a block diagram of leadframe surface measurement system 300according to one or more embodiments.

FIG. 4 shows flowchart 400 of a method of manufacturing a packageddevice using leadframe surface measurement system 300 according to oneor more embodiments.

FIG. 5 shows flowchart 500 of a method of evaluating a leadframe surfaceaccording to one or more embodiments.

FIG. 6 shows graph 600 showing comparison between brightness measurementaccording to leadframe surface brightness measurement method based onsingle wavelength reflection according to one or more embodiments of thepresent disclosure and brightness measurement according to ComparativeExamples 1 and 2 in which the brightness was measured using conventionaltechniques.

DETAILED DESCRIPTION

This disclosure pertains to a method of measuring brightness of asurface of a leadframe by irradiating light having a single wavelength.As used herein, single wavelength light means light having a singlewavelength. For example, the single wavelength light can be any of: redlight having a single wavelength within the wavelength range of 620-750nanometers (nm); green light having a single wavelength within thewavelength range of 495-570 nm; and blue light having a singlewavelength within the wavelength range of 450-495 nm. In some examples,the single wavelength light is emitted by a light emitting diode (LED).That is, instead of utilizing full visible wavelength to characterizecolor of the leadframe surface, this disclosure proposes irradiating theleadframe surface with only a single predetermined wavelength anddetecting reflection intensity of the leadframe surface responsive tothe incident single wavelength light. For example, the reflectionintensity represents a value of light power output for reflection lightat a particular wavelength and detected by an optical sensor. Thereflection intensity value can then be divided by a reflection intensityvalue of a standard known calibration piece to determine a reflectionratio. In some examples, a determination of whether to accept or rejectthe leadframe for further manufacturing operations is made based on thereflection ratio. More specifically, prior to measuring brightness of atarget leadframe, an optical sensor of a leadframe surface measurementapparatus is calibrated by irradiating light having the singlewavelength from a light source onto a standard calibration piece. Insome examples, the standard calibration piece is coated with a noblemetal such as gold or silver and represents peak brightness (reflectionintensity) associated with the single wavelength light source. Reflectedlight received from the standard calibration piece is received by alight receiver (e.g., photodiode) that photoelectrically convertsintensity of the reflected light into an electric signal. A processorthen converts the electric signal into a digital value and stores thedigital value as a predetermined reference reflection intensity value inmemory. In some examples, the target leadframe surface is thenirradiated with the light having the single wavelength and the reflectedlight from the leadframe surface is converted similarly to the reflectedlight from the standard calibration piece. A reflection ratio isdetermined based on the reflection intensity value of the leadframesurface and the predetermined reference reflection intensity value.

A determination regarding the leadframe surface being too dark or toobright is made based on the reflection ratio and predeterminedminimum/maximum brightness ratio thresholds, thereby effectivelyperforming incoming leadframe sheet quality control and preventingfailure of subsequently performed pattern recognition processes that arebased on measurement of leadframe surface brightness and color. In someexamples, light irradiated from the light source is pulsed light and thelight receiver is synchronized to receive the reflected light onlyduring the time period of emission of pulsed light by the light source.Thus, the light receiver only recognizes the emitting frequency of thesingle wavelength incident light and eliminates ambient light asbackground noise. Further, by calibrating intensity of light emittedfrom the light source and using light having the single wavelength,wavelength variation is eliminated and the same lighting condition isused for each leadframe brightness measurement.

FIG. 1A shows a perspective view of leadframe surface measurementapparatus 100 according to one or more embodiments. In some examples,leadframe surface measurement apparatus 100 is configured as anintegrated measurement jig having base 110 which movably supportsmeasurement stage 120. Measurement stage 120 is supported on base 110 byone or more guide rails 130 to enable mechanical movement of stage 120relative to base 110. In some examples, stage 120 is coupled to anXY-motor (not shown in FIG. 1A; see FIG. 3) and a Z-motor (not shown inFIG. 1A; see FIG. 3) to enable movement of stage in X-, Y-, andZ-directions along three orthogonal axes. Each of the XY-motor and theZ-motor is disposed between stage 120 and base 110 and is a linear motoror a rotary motor such as a servomotor or stepping motor to controlmovement of measurement stage 120. The motors are powered through powersupply provided inside base 110 to position measurement stage 120 at adesired positon in X-, Y-, and Z-directions.

Stage 120 includes sample tray 122, standard calibration piece 124, andknob 127 that secures sample tray 122 onto stage 120 by screwing onto ashaft extending from sample tray 122. Sample tray 122 securely holdsleadframe sheet S that is an electrically conductive sheet (made of ametal such as copper) with a plurality of integrally formed leadframeswhose brightness is to be measured by measurement apparatus 100. In oneembodiment, sample tray 122 and knob 127 are excluded and leadframesheet S is directly mounted on stage 120 for brightness measurement bymeasurement apparatus 100.

Standard calibration piece 124 is also secured to stage 120. Standardcalibration piece 124 has a metallic (mirror) coating that has very highreflectivity. For example, standard calibration piece 124 has a coatingof a noble metal such as gold, silver or aluminum or an alloy thereof.In one embodiment, standard calibration piece 124 is coated with silverthat has known reflectivity of greater than 98% when irradiated withlight having a wavelength in the range of 0.5 to 0.8 microns. Byirradiating standard calibration piece 124 coated with protected silverwith single wavelength light of approximately 630 nm, 98% absolutereflection will be achieved. As will be described in greater detaillater, a reflection intensity of standard calibration piece 124 isrecorded using measurement apparatus 100, thereby calibrating maximumreflection light intensity on a known reflection standard formeasurement apparatus 100. Reflectivity of leadframe sheet S is thencompared to this known piece.

Leadframe surface measurement apparatus 100 of FIG. 1A further includescantilever assembly 140 and optical sensor 150. As shown in FIG. 1A,cantilever assembly 140 is mounted on base 110 of measurement apparatus100 so that free end 142 of cantilever assembly 140 is positioned tooverhang measurement stage 120. Free end 142 of cantilever assembly 140houses distal end portions of a light source and a light receiver (notshown in FIG. 1A; see FIG. 3) of optical sensor 150 to irradiate apredetermined area of a surface of a leadframe of leadframe sheet S withlight from the light source, and to receive reflected light from thesurface of the leadframe of leadframe sheet S with the distal endportion of the light receiver at free end 142 of cantilever assembly140. As shown in the example of FIG. 1A, optical sensor 150 is mountedon cantilever assembly 140. Alternately, optical sensor 150 is housedinside or mounted on base 110, or may be provided separately from base110 and cantilever assembly 140. Optical sensor 150 is a fiber opticsensor, photoelectric sensor, laser sensor, and the like.

One set of one or more optical fiber cores is optically coupled at aproximal end thereof to the light source housed inside sensor body 152of optical sensor 150 and coupled at a distal end thereof to lens 154provided at free end 142 of cantilever assembly 140 to guide light fromthe light source to lens 154. Another set of one or more optical fibercores is further provided to be optically coupled at a proximal endthereof to a light receiver housed inside sensor body 152 of opticalsensor 150 and coupled at a distal end thereof to lens 154 to guidereflection light from the leadframe surface to the light receiver. Thus,both sets of one or more optical fiber cores extend from sensor body 152over laterally extending portion 141 of cantilever assembly 140 to beoptically coupled to lens 154 at free end 142.

The light source of optical sensor 150 emits light having a singlepredetermined wavelength for leadframe surface brightness measurement.The light source is an LED, a halogen lamp, a laser light source and thelike. For example, the light source is an LED emitting red light at asingle wavelength of approximately 630 nanometers (nm). Alternately, thelight source is an LED emitting blue or green single wavelength light.Wavelength of light emitted from the light source for brightnessmeasurement depends on the light wavelength that is used for patternrecognition in subsequent steps of the package assembly process.

In some examples, the light source of optical sensor 150 emits pulsedlight at periodic, random or irregular intervals. A time period ofemission of the pulse light of the light source of optical sensor 150 isless than a second. The light receiver of optical sensor 150 receivesreflected light corresponding to only the single wavelength lightemitted by the light source. For example, the light receiver is aphotodiode that photoelectrically converts received reflected light intoan electric signal. Light reception by the light receiver of opticalsensor 150 is synchronized with the pulsed light emission by the lightsource so that the light receiver operates to receive reflected lightonly during the interval when the light source emits the singlewavelength light. Thus, when the light source emits the singlewavelength light during a first time period and ceases the emissionduring a second time period following the first time period, operationof the light receiver is synchronized so that the light receiveroperates to receive reflected light only during the first time periodbut not during the second time period. Synchronizing light reception asdescribed above results in optical sensor 150 emitting light at acertain frequency and the light receiver detecting only the reflectedlight having the same frequency as the emitted light and not detectingother light which may be background light or noise. This results inbackground light not affecting reading of the reflection light andelimination of background noise. As a result, brightness measurementaccuracy of measurement apparatus 100 is improved.

FIG. 1B shows an enlarged perspective view of light irradiationoperation conducted by leadframe surface measurement apparatus 100according to one or more embodiments. As shown in FIG. 1B, light isemitted from the distal end portion of the light source of opticalsensor 150 at free end 142 of cantilever assembly 140. Lens 154 isprovided at free end 142 of cantilever assembly 140 so as to bepositioned on an optical path between the distal end portion of thelight source and a surface of one of the leadframes of leadframe sheet Smounted on sample tray 122 of measurement apparatus 100. Singlewavelength light emitted from the light source of optical sensor 150passes through lens 154 and is irradiated on the leadframe surface ofsheet S and reflected light from the leadframe surface of sheet S isagain transmitted through lens 154 to be incident on the distal endportion of the light receiver of optical sensor 150. Lens 154 acts as afocus lens to reduce a beam size (spot size) of light emitted from theoptical fiber core of the light source at the distal end portion thereofto focus the light onto a predetermined area on a surface of one of theleadframes of leadframe sheet S.

For example, as shown in FIG. 1B, the predetermined area is within aroughly rectangular area of die stage D on an upper surface of theleadframe where a semiconductor chip is to be mounted, with a pluralityof leads of the leadframe being arranged outside of the area of diestage D and being electrically connected with electrodes of thesemiconductor chip. In one embodiment, the predetermined area is at acenter of die stage D. Stage 120 is adjusted in the X-, Y-, andZ-directions using the XY- and Z-motors to position the predeterminedarea on the surface of the leadframe on an optical axis of lens 154 toirradiate the predetermined area. In one embodiment, stage 120 isadjusted in the Z-direction to keep a focus distance between a lowersurface of lens 154 and upper surface of the leadframe to 7 millimeters(mm) and lens 154 is adjusted to reduce the spot size of the irradiationlight to 0.4 millimeters while the light source of optical sensor 150emits red LED light at approximately 630 nm. In general, to ensureproper measurement of brightness of the surface of the leadframe, lens154 is operated to adjust the spot size of emitted light so that thespot size is smaller than the area of die stage D of the leadframe ofleadframe sheet S.

Reflected light from the surface of the leadframe is received by thelight receiver of optical sensor 150 to measure a reflection intensity(brightness) value of the received light. FIG. 2 shows graph 200A of anincident single wavelength and graph 200B of reflection intensityaccording to one or more embodiments. Abscissa in each of graphs 200Aand 200B represents wavelength (nm) of incident or reflection light andordinate represents a normalized power spectrum (milliwatt (mW))indicating light power output at a particular wavelength for incident orreflection light.

As shown in graph 200A when red light having a single predeterminedwavelength of approximately 630 nm is emitted from the light source ofoptical sensor 150, the light power output at the peak wavelength is102.960 mW, which is equated to 1.0 on the normalized spectrum on theY-axis. When this light having the single wavelength and power outputcharacteristics as illustrated in incident single wavelength graph 200Ais incident on the predetermined area of the leadframe surface ofleadframe sheet S, the light receiver of optical sensor 150 detectsreflection light having wavelength and power output characteristics asillustrated in graph 200B shown in FIG. 2.

As shown in graph 200B, the reflection light will have a certain amountof loss compared to the incident single wavelength light due toleadframe surface roughness, and as a result, intensity of the reflectedlight will be lower than the incident light. The light power output onthe normalized spectrum for the reflected light is approximately 0.6 onthe Y-axis as illustrated in reflection intensity graph 200B. In oneembodiment, light receiver of optical sensor 150 photoelectricallyconverts reflected light received by a photodiode into an electricsignal. The optical sensor 150 or a processor (see FIG. 3) furtherconverts the electric signal into a digital value (reflection intensityvalue or normalized spectrum value). By comparing the normalizedspectrum value corresponding to standard calibration piece 124 with thenormalized spectrum value of the predetermined area of the targetleadframe surface of leadframe sheet S, brightness of the leadframesurface is accurately measured so that subtle variations of the colorand brightness of leadframe surfaces can be quantified with goodrepeatability and reproducibility.

FIG. 3 shows a high-level block diagram of leadframe surface measurementsystem 300 that is used to implement one or more disclosed embodiments.Only relevant portions of leadframe surface measurement system 300 areillustrated in FIG. 3. Further, detailed description of components ofleadframe surface measurement system 300 that have been alreadydescribed in detail in connection with leadframe surface measurementapparatus 100 of FIG. 1A is omitted here. Leadframe surface measurementsystem 300 includes leadframe surface measurement apparatus 100 (seeFIG. 1A) which includes measurement stage 120, XY-motor 126, Z-motor128, light source 156, and light receiver 158. Leadframe surfacemeasurement system 300 further includes one or more input devices 330,such as a keyboard, mouse, or touchpad and one or more output devices315, such as displays, or speakers for audio. Some devices may beconfigured as input/output devices as well (e.g., a network interface ortouchscreen display).

As illustrated in the example of FIG. 3, leadframe surface measurementsystem 300 includes processor 305 that contains one or more hardwareprocessors, where each hardware processor has a single or multipleprocessor cores. In one embodiment, the processor 305 includes at leastone shared cache that stores data (e.g., computing instructions) thatare utilized by one or more other components of processor 305. Forexample, the shared cache is a locally cached data stored in a memoryfor faster access by components of the processing elements that make upprocessor 305. Examples of processors include, but are not limited to acentral processing unit (CPU) a microprocessor.

FIG. 3 illustrates that memory 310 is operatively and communicativelycoupled to processor 305. Memory 310 is a non-transitory mediumconfigured to store various types of data. For example, memory 310includes one or more storage devices 320 that comprise a non-volatilestorage device and/or volatile memory. Volatile memory, such as randomaccess memory (RAM), can be any suitable non-permanent storage device.The non-volatile storage devices 320 can include one or more diskdrives, optical drives, solid-state drives (SSDs), tap drives, flashmemory, read only memory (ROM), and/or any other type memory designed tomaintain data for a duration time after a power loss or shut downoperation. In certain instances, the non-volatile storage devices 320are used to store overflow data if allocated RAM is not large enough tohold all working data. The non-volatile storage devices 320 are alsoused to store programs that are loaded into the RAM when such programsare selected for execution.

Software programs may be developed, encoded, and compiled in a varietyof computing languages for a variety of software platforms and/oroperating systems and subsequently loaded and executed by processor 305.In one embodiment, the compiling process of the software program maytransform program code written in a programming language to anothercomputer language such that the processor 305 is able to execute theprogramming code. For example, the compiling process of the softwareprogram may generate an executable program that provides encodedinstructions (e.g., machine code instructions) for processor 305 toaccomplish specific, non-generic, particular computing functions.

After the compiling process, the encoded instructions may then be loadedas computer executable instructions or process steps to processor 305from storage 320, from memory 310, and/or embedded within processor 305(e.g., via a cache or on-board ROM). Processor 305 is configured toexecute the stored instructions or process steps in order to performinstructions or process steps to transform the computing device into anon-generic, particular, specially programmed machine or apparatus.Stored data, e.g., data stored by a storage device 320, is accessed byprocessor 305 during the execution of computer executable instructionsor process steps to instruct and operate one or more components withinthe leadframe surface measurement system 300.

A user interface (e.g., output devices 315 and input devices 330) caninclude a display, positional input device (such as a mouse, touchpad,touchscreen, or the like), keyboard, or other forms of user input andoutput devices. The user interface components are communicativelycoupled to processor 305. When the output device is or includes adisplay, the display can be implemented in various ways, including by aliquid crystal display (LCD) or a cathode-ray tube (CRT) or lightemitting diode (LED) display, such as an OLED display. In some examples,leadframe surface measurement system 300 comprises other components wellknown in the art, such as sensors, powers sources, and/oranalog-to-digital converters, not explicitly shown in FIG. 3. One ormore of processors 305, input devices 330, output devices 315, memory310 and storage 320 are provided within leadframe surface measurementapparatus 100 or may be communicatively coupled to leadframe surfacemeasurement apparatus 100 over a network.

FIG. 4 shows flowchart 400 of a method of manufacturing a packageddevice using leadframe surface measurement system 300 according to oneor more embodiments. Flowchart 400 begins at block 410 with processor305 conducting leadframe surface evaluation to measure brightness of aleadframe surface of leadframe sheet S. Operations performed at block410 are described in detail below in connection with flowchart 500 ofFIG. 5.

At block 420, semiconductor chips (dies) are individually mounted oneach die stage D of each leadframe of leadframe sheet S responsive to adetermination at block 410 that the brightness of the leadframe surfaceis acceptable for a further semiconductor chip package assemblyoperation. At block 430, a wire bonding process of attaching each die toa corresponding leadframe on sheet S is performed by electricallyconnecting connection pads on the die with pads on the leadframe with,for example, copper wires. Connecting the die to the leadframe bringsconnections of the die to an outer area of the leadframe, thereby makingit easier to solder the die and leadframe structure onto a circuitboard. At block 440, a molding operation of applying a mold compoundover the die and leadframe structure is performed. In one embodiment,the mold compound is applied on the die and leadframe structure and thecompound is cured using thermal or ultraviolet radiation so as to hardenand protect the die. Tips of the leadframe remain exposed after thecuring to enable the resulting chip to be soldered onto a circuit board.Finally, at block 450, the molded and electrically connected packages ofdies and leadframes on leadframe sheet S are singulated (separated) intoindividual packaged devices. In one embodiment, the semiconductor chippackages may be singulated using a saw or laser.

FIG. 5 shows flowchart 500 of a method of evaluating a leadframe surfacecorresponding to block 410 of flowchart 400 according to one or moreembodiments. Flowchart 500 begins at block 510 with processor 305conducting a calibration operation of measurement apparatus 100 withstandard calibration piece 124. Processor 305 accesses programs and datastored in storage 320 to perform the calibration operation. For example,processor 305 obtains XYZ position information of standard calibrationpiece 124 mounted on measurement stage 120 and execute instructions tooperate XY-motor 126 and Z-motor 128 to position standard calibrationpiece 124 on an optical axis of lens 154 for brightness measurement andcalibration. Processor 305 then executes instructions to controloperations of light source 156 and light receiver 158 to irradiatestandard calibration piece 124 with single wavelength light and obtainreflection light. Processor 305 further controls operations of lightsource 156 and light receiver 158 to irradiate the single wavelengthlight as a pulsed light and synchronize operation of light receiver 158with the pulsed light emission of light source 156 to eliminate effectsof background light, thereby obtaining a more accurate brightnessmeasurement value standard calibration piece 124. In some examples,processor 305 then operates an analog-to-digital converter (now shown)to convert the electric signal obtained from light receiver 158 into adigital value and store the digital value as a predetermined referencereflection intensity value in storage 320. In some examples, calibrationoperation at block 510 is performed only once when apparatus 100 ispowered ON for brightness measurement. Actual brightness measurementoperation for one or more leadframe surfaces on one or more sheets S isthen performed once the apparatus 100 has been calibrated at block 510.

At block 520, processor 305 obtains XYZ position information of apredetermined area on a leadframe surface of leadframe sheet S mountedon sample tray 122 that is to be subject to the brightness measurementoperation. Processor 305 executes instructions to operate XY-motor 126and Z-motor 128 to position the predetermined area on the optical axisof lens 154 for brightness measurement.

At block 530, processor 305 controls light source 156 to irradiatesingle wavelength light onto the predetermined area on the leadframesurface of sheet S, and at block 540, processor 305 controls lightreceiver 158 to receive reflected light corresponding to the singlewavelength light incident on the predetermined area on the surface ofthe leadframe of leadframe sheet S. Processor 305 further controlsoperations of light source 156 and light receiver 158 to irradiate thesingle wavelength light as a pulsed light and synchronizes operation oflight receiver 158 with the pulsed light emission of light source 156 toeliminate effects of background light, thereby obtaining a more accuratebrightness measurement value of the predetermined area of leadframesheet S. In some examples, processor 305 then operates ananalog-to-digital converter (now shown) to convert the electric signalobtained from light receiver 158 and corresponding to the reflectionlight intensity of the predetermined area of the surface of theleadframe of leadframe sheet S into a digital value and stores thedigital value as a reflection intensity value in storage 320.

At block 550, processor 305 calculates a reflection ratio based on thestored reflection intensity value and the stored predetermined referencereflection intensity value. For example, processor 305 divides thereflection intensity value of target leadframe surface with thepredetermined reference reflection intensity value of standardcalibration piece 124 to calculate the reflection ratio. The valuecalculated at block 550 is expressed in percentage form (i.e., 1% to100%) or as a value representing a result of the division.

At block 560, processor 305 determines whether the calculated reflectionratio is within a predetermined permissible reflection ratio range.Information regarding the permissible reflection ratio range is storedin storage 320 and is predetermined for each type of leadframe sheet Swhose brightness is to be measured with measurement apparatus 100. Forexample, a leadframe brightness is considered permissible if thereflection intensity value of the leadframe surface is more than 10% ofthe stored predetermined reference reflection intensity value ofstandard calibration piece 124. Thus, if the calculated reflection ratiois lower than a minimum brightness ratio threshold (“NO” at block 560),processor 305 determines that the leadframe surface is too dark andtherefore, the leadframe is unusable for subsequent semiconductorpackage assembly operations (block 570). Conversely, if the calculatedreflection ratio is higher than a maximum brightness ratio threshold(“NO” at block 560), processor 305 determines that the leadframe surfaceis too bright and therefore, the leadframe is unusable for subsequentsemiconductor package assembly operations (block 570). In some examples,processor 305 indicates the leadframe is unacceptable for amanufacturing operation at block 570 by displaying a result of thedetermination at block 560 on a display.

If, on the other hand, processor 305 determines that the calculatedreflection ratio is within the predetermined permissible reflectionratio range (“YES” at block 560), processor 305 determines that theleadframe surface brightness is within an acceptable operating range,and therefore, the leadframe is usable for subsequent semiconductorpackage assembly operations (block 580). In some examples, processor 305indicates the leadframe is acceptable for a manufacturing operation atblock 580 by displaying a result of the determination at block 560 on adisplay. In one embodiment, processor 305 executes instructions storedin storage 320 to perform the steps of the leadframe surface evaluationmethod illustrated in flowchart 500 of FIG. 5 automatically, without anyoperation by a user. Thus, for example, processor 305 automaticallycontrols operations of one or more of stage 120, XY-motor 126, Z-motor128, light source 156, and/or light receiver 158 to perform thecalibration and brightness measurement operations. Processor 305 thenautomatically outputs a result of the brightness measurement operationto a user by, for example, displaying a result on a display 315 or anaudible signal. Alternatively, one or more of the operations offlowchart 500 are performed manually. In one embodiment, the operationsof flowchart 500 of FIG. 5 can be used in in-line monitoring of anassembly line of a die bonder. Brightness can then be measured at thepredetermined area of the surface of each leadframe for quick inspectionand “pass” or “fail” determination.

Experiments have been conducted to test viability of the leadframesurface brightness measurement method based on single wavelengthreflection according to the present disclosure. A Six Sigma GageRepeatability and Reproducibility (GRR) study was performed to assessthe leadframe surface brightness measurement method according to thepresent disclosure by measuring the amount of variation in themeasurement system arising from sources like particular measurementapparatus used or personnel taking the measurement. The results showedthat the overall GRR for the leadframe surface brightness measurementmethod according to the present disclosure was less than 10% with fastexamination time (e.g., measurement time of less than one second permeasurement).

Conventional techniques for measuring and quantifying variations inleadframe surface brightness and color include mean grayscale valuecalculation method and XYZ tristimulus measurement method. In the meangrayscale value calculation method an image of a leadframe surface takenunder a microscope with fixed light intensity is cropped to focus on aleadframe die stage surface area, the cropped image is analyzed togenerate a histogram of the cropped area and mean grayscale value iscalculated for the cropped area based on the histogram to determine amean brightness value of the leadframe surface. In the XYZ tristimulusmethod, a halogen lamp is used as a light source to detect reflection inmultiple wavelengths in a wavelength range of 380 nm-780 nm. Reflectionspectrum R(λ) is converted to XYZ by x(λ), y(λ), z(λ) color matchingfunctions and X, Y, Z values can be judged as red/green/blue reflectionintensity values to detect a color of the leadframe surface in unit GAM.However, with the conventional mean grayscale value calculation method,background lighting introduces too much variation in the mean grayscalecalculation thereby lowering reliability and reproducibility of measuredgrayscale values. Further, with the XYZ tristimulus method, brightnessmeasurement for a roughened leadframe surface is not very consistent andis susceptible to various hardware and software variations and thereforenot feasible. Inventors of the present application conducted experimentson different batches of leadframe sheets having the same specificationsreceived over an extended period of time and determined that theleadframe surface brightness measurement method based on singlewavelength reflection according to the present disclosure has bettercorrelation to visual appearance (brightness) of the leadframe surfacethan the above described conventional techniques. As shown in graph 600of FIG. 6, brightness measurement according to the leadframe surfacebrightness measurement method based on single wavelength reflectionaccording to the present disclosure has better correlation to actualleadframe surface brightness than measurement according to ComparativeExamples 1 and 2 using conventional techniques involving colormeasurement based on measured RGB reflection values using XYZtristimulus method or mean grayscale calculation method.

Certain terms have been used throughout this description and claims torefer to particular system components. As one skilled in the art willappreciate, different parties may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In this disclosure and claims, theterms “including” and “comprising” are used in an open-ended fashion,and thus should be interpreted to mean “including, but not limited to .. . .” Also, the term “couple” or “couples” is intended to mean eitheran indirect or direct wired or wireless connection. Thus, if a firstdevice couples to a second device, that connection may be through adirect connection or through an indirect connection via other devicesand connections. The recitation “based on” is intended to mean “based atleast in part on.” Therefore, if X is based on Y, X may be a function ofY and any number of other factors. The recitation “approximately” beforethe recitation of a value is intended to cover all values within therange of ±10% of the value.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

1-20. (canceled)
 21. A method of manufacturing a packaged device, themethod comprising: mounting a semiconductor chip on a leadframeresponsive to a determination that a brightness ratio of a predeterminedarea on a surface of the leadframe is within a predetermined range;electrically connecting pads on the semiconductor chip with pads on theleadframe; applying a molding compound on the semiconductor chip and theleadframe and curing the molding compound; and singulating each of aplurality of the leadframes of a leadframe sheet to manufacture aplurality of packaged devices.
 22. The method of manufacturing thepackaged device according to claim 21, further comprising: positioningthe leadframe on a measurement apparatus at a first predetermineddistance relative to an end portion of a light source of an opticalsensor; irradiating the predetermined area on the surface of theleadframe with the light having the single predetermined wavelength fromthe light source; receiving, with a light receiver of the opticalsensor, reflected light from the predetermined area on the surface ofthe leadframe, and converting the reflected light into an electricsignal; determining a reflection intensity value of the predeterminedarea on the surface of the leadframe based on the electric signal; andcalculating a reflection ratio of the predetermined area on the surfaceof the leadframe based on the reflection intensity value and apredetermined reference reflection intensity value associated with thelight source.
 23. The method of manufacturing the packaged deviceaccording to claim 22, further comprising: positioning a calibrationpiece on the measurement apparatus and irradiating the calibration piecewith the light having the single predetermined wavelength; receiving,with the light receiver of the optical sensor, reflected light from thecalibration piece; determining the predetermined reference reflectionintensity value based on the reflected light from the calibration piece;and dividing the reflection intensity value by the predeterminedreference reflection intensity value to calculate the reflection ratio.24. The method of manufacturing the packaged device according to claim23, wherein the calibration piece is coated with one or more of gold,silver, and aluminum.
 25. The method of manufacturing the packageddevice according to claim 22, wherein the reflected light from thepredetermined area on the surface of the leadframe represents abrightness of the surface of the leadframe; and wherein the methodfurther comprises indicating the brightness of the surface of theleadframe as being within a permissible range when the reflection ratiois higher than a predetermined minimum brightness ratio threshold. 26.The method of manufacturing the packaged device according to claim 22,wherein the light source is a pulsed light source, and wherein themethod further comprises: irradiating the predetermined area on thesurface of the leadframe with the light having the single predeterminedwavelength during a first time period; ceasing irradiating thepredetermined area on the surface of the leadframe with the light havingthe single predetermined wavelength during a second time periodfollowing the first time period; and synchronizing an operation of thelight receiver with an operation of the light source such that the lightreceiver operates to receive the reflected light during the first timeperiod but not during the second time period.
 27. The method ofmanufacturing the packaged device according to claim 26, wherein thelight source is a pulsed light emitting diode (LED) that emits red lightat 630 nanometers.
 28. The method of manufacturing the packaged deviceaccording to claim 22, wherein the optical sensor is a fiber opticsensor, and wherein the light source comprises an LED and a firstoptical fiber guiding the light from the LED to the distal end portionof the light source, and wherein the light receiver comprises aphotodiode and a second optical fiber guiding the reflected light from adistal end portion of the light receiver to the photodiode.
 29. Themethod of manufacturing the packaged device according to claim 22,further comprising: positioning a lens in an optical path between thedistal end portion of the light source and the predetermined area on thesurface of the leadframe on the measurement apparatus; and adjusting afocus positon of the lens to focus the light from the light source onthe predetermined area on the surface of the leadframe.
 30. The methodof manufacturing the packaged device according to claim 22, wherein thelight receiver is a photodiode.
 31. The method of manufacturing thepackaged device according to claim 21, wherein the irradiating light isa red light having a single wavelength within the wavelength range of620-750 nanometers (nm).
 32. The method of manufacturing the packageddevice according to claim 21, wherein the irradiating light is a greenlight having a single wavelength within the wavelength range of 495-570nanometers (nm).
 33. The method of manufacturing the packaged deviceaccording to claim 22, wherein the irradiating light is a blue lighthaving a single wavelength within the wavelength range of 430-495nanometers (nm).
 34. A method of manufacturing packaged devices, themethod comprising: mounting semiconductor chips on leadframes responsiveto a determination that a brightness ratio of an area on a surface ofthe leadframes is within a predetermined range; electrically connectingpads on the semiconductor chips with pads on the leadframes; applying amolding compound on the semiconductor chips and the leadframes andcuring the molding compound; and singulating each of a plurality of theleadframes to manufacture a plurality of packaged devices.
 35. A methodof manufacturing packaged devices, the method comprising: mountingsemiconductor chips on leadframes responsive to a determination that abrightness ratio of an area on a surface of the leadframes is within apredetermined range; electrically connecting pads on the semiconductorchips with pads on the leadframes; and applying a molding compound onthe semiconductor chips and the leadframes and curing the moldingcompound
 36. A method of manufacturing a packaged device, the methodcomprising: mounting a semiconductor chip on a leadframe responsive to adetermination that a brightness ratio of an area on a surface of theleadframe is within a predetermined range; electrically connecting padson the semiconductor chip with pads on the leadframe; and applying amolding compound on the semiconductor chip and the leadframe and curingthe molding compound.